Resolving the Issue of Selected Item is Null in Xamarin.Forms CollectionView

Описание: Discover how to troubleshoot the issue of a null `Selected Item` in Xamarin.Forms CollectionView when using `TapGestureRecognizer` effectively in your applications.
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This video is based on the question https://stackoverflow.com/q/66340661/ asked by the user 'Rajzer' ( https://stackoverflow.com/u/10922741/ ) and on the answer https://stackoverflow.com/a/66382087/ provided by the user 'Rajzer' ( https://stackoverflow.com/u/10922741/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

Developing applications using Xamarin.Forms often involves working with CollectionViews to display data in a user-friendly manner. However, one common issue developers run into is when the selected item turns out to be null, possibly leading to unexpected behaviors in the app. In this guide, we'll explore the root cause of this issue and provide a practical solution to get the selected item functionality working seamlessly in your app.

The Problem

In a sample application, the developer encounters a scenario where the SelectedPhoto object in the ViewModel remains null even after attempting to select an item from the CollectionView. This can be frustrating, especially when trying to implement the command to retrieve details about the selected photo. The developer's current approach utilizes a Grid.TapGestureRecognizer along with a LoadSelectedPhotoCommand, but unfortunately, the SelectedPhoto remains null, indicating that the item is not being clicked properly.

Code Snapshot

Here's a brief overview of the significant parts of the code in the XAML and ViewModel that are relevant to the issue:

[[See Video to Reveal this Text or Code Snippet]]

In the above code, although the TapGestureRecognizer is defined, the item selection is not being captured correctly.

The Solution

Upon investigating the problem, it becomes clear that the Grid.TapGesture is overriding the SelectionMode for the CollectionView, leading to the SelectedPhoto being null when an item is tapped. To resolve this issue, we'll modify the CollectionView setup slightly and remove the TapGestureRecognizer. Here’s how:

Step 1: Remove TapGestureRecognizer

By removing the Grid.GestureRecognizers section from the item template, we allow the CollectionView to correctly handle item selection. The collection view's item selection feature inherently manages tap interactions.

Updated XAML Code

Here's how your revised CollectionView should look:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Retaining Command Logic

To ensure that you still retrieve details of the selected photo, you can invoke your command directly from the property changed event of the SelectedPhoto. This can be done like so in your ViewModel:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By making these adjustments, you can effectively manage selections in your Xamarin.Forms application without running into the Selected Item is null issue. This tweak allows the CollectionView to work as intended while retaining your ability to perform actions based on the selected photo. Properly structuring your XAML and understanding the interaction between various components is key to delivering a smooth user experience.

Implement these changes in your project, and you'll find that the SelectedPhoto reflects the expected, non-null value upon item selection! If you have further questions or run into additional issues, feel free to reach out or explore the Xamarin.Forms documentation.